1. Field of the Invention
The present invention relates to an image formation apparatus in which a latent electrostatic image is formed on an electrophotographic photoconductor or an electrostatic recording member by an electrostatic recording method, and in particular to an image formation apparatus comprising a means for decomposing ozone generated in the apparatus by intentionally bringing ozone into contact with a mist of, for example, a carrier liquid for a liquid developer, and a release agent applied to a heat-application roller in an image fixing unit.
2. Discussion of Background
In an image formation apparatus employing an electrostatic recording method, namely, an electrostatic copying apparatus, a latent electrostatic image is formed on an electrophotographic photoconductor or an electrostatic recording member. The latent electrostatic image is developed into a visible toner image with a wet- or dry-type developer and the toner image thus obtained is electrostatically transferred to a transfer sheet and fixed thereto by using a heat-application roller. Thus, the toner image can be fixed to the transfer sheet.
FIG. 1 shows a conventional dry-type electrophotographic copying apparatus. In FIG. 1, a photoconductive drum 3 is rotatably driven in the clockwise direction. An original (not shown) is placed on a contact glass 1, with an image-bearing side thereof in contact with the contact glass 1. The surface of the photoconductive drum 3 is uniformly charged by an electric charger 10 and exposed to the light images which are converted from the original images of the original by an optical scanning system 2. As a result, the latent electrostatic images corresponding to the original images are formed on the surface of the photoconductive drum 3. The latent electrostatic images are developed to visible toner images with a dry-type developer in a development unit 12. The visible toner images thus formed on the photo-conductive drum 3 are transferred via a transfer charger 14 to a transfer sheet which is supplied from a paper supply cassette 4 or 5. The transfer sheet is separated from the photoconductive drum 3 using a separation charger 15 and transported to an image fixing unit through a conveyor belt 19. In the image fixing unit, the toner images transferred on the transfer sheet are thermally fixed thereto by causing the sheet to pass between a pair of image fixing rollers 20. After the completion of the image fixing, the transfer sheet is discharged onto a copy tray 22.
In FIG. 1, reference numerals 6 and 7 indicate paper supply rollers; reference numeral 8, a resist roller; reference numeral 9, paper carrier roller; reference numeral 11, an eraser; reference numeral 13, a quenching lamp for image transfer; reference numeral 16, a separation pawl; reference numeral 17, a fur brush; reference numeral 18, a quenching lamp; reference numeral 21, a pair of paper discharging rollers; reference numeral 30, a toner concentration detector; and reference numeral 31, a slit.
As mentioned above, the photoconductor or electrostatic recording member is charged to a predetermined polarity by a corona charger in the course of the latent electrostatic image formation process, and the toner images formed on the photoconductor or electrostatic recording member are transferred to the transfer sheet using the corona charger. This results in the generation of ozone in the apparatus. In addition to the corona charger, a quenching unit is provided in order to constantly produce high quality images in a high-speed image formation apparatus or an image formation apparatus applicable to the wide-width image formation. When the quenching unit is in operation, electrical discharging takes place and ozone is generated by the electrical discharging. Thus, the quenching unit is also a source of generating ozone. Accordingly, ozone is unfavorably generated and built-up in the image formation apparatus during the operation thereof.
When the concentration of the ozone reaches 0.02 ppm or more, some people feel a foreign odor. At a concentration of 0.1 ppm or more, the ozone gives an unpleasant feeling and it cannot be ignored from the viewpoint of hygiene.
In addition to the above, when the inside of the image formation apparatus is exposed to the ozone at a concentration of 0.1 ppm or more for an extended period of time, the constituent parts of the image formation apparatus such as a rubber member deteriorate, and the characteristics of a photoconductive layer of the photoconductor are degraded because of oxidation caused by the ozone.
To remove the ozone generated in the image formation apparatus, an ozone decomposing unit employing an ozone decomposing agent is conventionally proposed. However, the ozone decomposing unit makes it difficult to reduce the size of the image formation apparatus. Furthermore, when such an ozone decomposing unit is employed, the ozone decomposing agent has to be replenished and the maintenance of the ozone decomposing unit is necessary, which increases the cost of the image formation apparatus as a whole.
When a wet-type electrophotographic copying apparatus is compared with a dry-type electrophotographic copying apparatus, the amount of ozone discharged from the wet-type copying apparatus is smaller. This is possibly because a solvent used as a carrier liquid for a liquid developer vaporizes in a development unit to become a mist. During the development of latent electrostatic images with a liquid developer and the transfer of the developed images after development, the carrier liquid for the liquid developer which has deposited on the photoconductive drum or the transfer sheet also vaporizes in the apparatus to become a mist. When the mist of the carrier liquid hanging in the apparatus comes into contact with ozone generated in the image formation apparatus, part of the ozone is decomposed to oxygen. Furthermore, a release agent which is applied to a heated image-fixing roller vaporizes and turns into a mist during the thermal image fixing. When the solvent mist of the release agent comes into contact with ozone, the ozone is slightly decomposed.
In a dry-type electrophotographic copying apparatus, only a release agent can become a solvent mist, so that the amount of the solvent mist generated therefrom is small. Thus, ozone is hardly decomposed by the mist of the conventional release agent in the dry-type copying apparatus.
Conventionally, the decomposition of ozone depends on the degree of the spontaneous contact of the mist of a solvent, such as a carrier liquid for the liquid developer, with the ozone, both of which are merely in suspension in the air in the apparatus, and the solvent mist is not intentionally brought into contact with the ozone by use of a special means. Therefore, the ozone is hardly decomposed.
The liquid developer which is prepared by dispersing toner particles in an aliphatic hydrocarbon such as nonane, decane, isododecane and isooctane is conventionally used in the wet-type image formation apparatus. These aliphatic hydrocarbons are excellent in the image fixing performance, so that they are widely used as the carrier liquids for the liquid developer. However, the aliphatic hydrocarbons have particular odors and are readily oxidized to produce an offensive odor when heated in the image fixing operation.
As previously mentioned, a heat-application roller is generally employed in the image fixing unit of the image formation apparatus. A release agent, such as a silicone oil, is applied to the surface of the heat-application roller in order to easily separate a transfer sheet from the heat-application roller after the image fixing operation. The silicone oil used as the release agent vaporizes and becomes a solvent mist by the application of heat in the image fixing operation and goes up in a white smoke, which makes an unfavorable impression upon the users of this kind of image formation apparatus. Therefore, the silicone oil with a small volatile content, usually less than 0.5 wt. % is conventionally used.
To prepare a silicone oil with a small volatile content, however, a costly refining process is required. Furthermore, when the silicone oil is applied to the surface of the heat-application roller, a release agent application pad is generally used. Since the release agent application pad impregnated with the silicone oil is disposed in pressure contact with the surface of the heat-application roller, the silicone oil considerably evaporates and is wasted even when the image forming process is not carried out. It is desired that the silicone oil be not only effectively used as the release agent for the heat-application roller, but also efficiently utilized for decomposing the aforementioned ozone.